<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<h1>0</h1>
<h2>0</h2>

<script>
  setInterval(f,1000);
let count =0;
function f() {
  count++;
  let h = document.querySelector("h1");
  h.innerText =count;
}

/*第二种定时器的方法*/
  let x = 0;
  let timer = setInterval(function () {
    x++;
    let h = document.querySelector("h2");
    h.innerText = x;
    if (x>50){
      clearInterval(timer);
    }
  },100);

  /*只执行一次的电池*/
  setTimeout(function () {
    x= 10;
  },3000);


</script>
</body>
</html>